java

Java & Kotlin Conventions

JVM language coding conventions complementing the TDD and Clean Code skills. We use modern language features to reduce boiler plate and get more to the point.

Java Version

When you need to know the latest Java version (e.g. for new projects, upgrades, or Dockerfiles), query the Adoptium API:

https://api.adoptium.net/v3/info/available_releases

Use most_recent_feature_release (latest GA) by default. Use most_recent_lts only when explicitly asked for LTS.

Code Style

Logic Expressions

• Try to prevent negating expressions, e.g., instead of a != b ? doX() : doY() use a == b ? doY() : doX().

Line Breaks

• Annotations can often go in the same line as the field or method they apply to.
  • Java: @Override void foo() { or @Test void should() {
  • Kotlin: override fun foo() { or @Test fun should() {

Local Type Inference

Java: Use var for local variable type inference where the type is clear from context.

var users = userRepository.findAll();
var count = items.size();

Kotlin: Type inference is the default. Prefer val (immutable) over var (mutable); only use var when the variable must be reassigned.

val users = userRepository.findAll()
var count = items.size  // only if count is later mutated

Static Imports (Java) / Imports (Kotlin)

Java: Prefer static imports when they do not reduce readability. This includes constants like MediaType.APPLICATION_JSON. The context is most often sufficient to understand what it is, e.g., @Produces(APPLICATION_JSON). Exception: do not statically import List.of(...), Map.of(...), or the like, as a method name like of doesn't say, what it does. The number of usages of the import is not relevant!

import static jakarta.ws.rs.core.MediaType.APPLICATION_JSON;
import static org.assertj.core.api.BDDAssertions.then;
import static org.mockito.BDDMockito.given;

Kotlin: There are no static imports. Import top-level functions and object/companion members directly. The same readability rule applies — import short, context-sufficient names; avoid importing bare of.